The invention relates to a glass-ceramic composition having a high fracture strength and especially suitable for sealing to chromium bearing iron or nickel base alloys.
In applications requiring the passing of electrical leads through an insulator wall such as in a vacuum tube or an explosive actuator, there are problems in achieving a good seal between the insulator and the metal, mismatches of thermal expansivity, and a need for a high strength material to withstand high stresses. In the past, in designing seals for stainless steel or the like, designers have been restricted to either directly sealing to glass or to brazing to a ceramic member. In sealing to glass, a special process was required to preoxidize the surface of the steel such it would be wet by the molten glass. In sealing to ceramic it was generally necessary to machine the fired ceramic to a desired configuration and utilize multiple firings to deposit the braze material on the ceramic and metal surfaces to be sealed. These multiple step processes generally were difficult to accomplish and economically undesirable.